Salt melts as heat transfer media



Patented Aug. 13, 1940 UNITED ST TES PATENT ppm:

- can:

Walter Frankfort-on-the-Main, Germany,

Manor to Dcntsche Gold and Silber Seheideanstalt vormals Bossier, Frankfort-on-the- Main, Germany, a corporation of Germany No Drawing. Application April 24, 1959, Serial No. 269,815. n Germany April so, 1938 6 Claims. (Cl. 252) .5 such equipment, especially those constructed of iron or steel. The invention relates particularly to processes and equipment in which the apparatus, vessels, or parts thereof, are subjected to indirect heating, using fused salt compositions as 10 heat transfer media. I

It is known that when carrying out processes of the aforementioned type, much premature corrosion of the metal parts coming in contact with the heat transfer medium .occurs. The corrosion may be due to variouscauses such as oxidation, e. g. by atmospheric oxygen present in small amounts in the liquid, reaction of corroding constituents, by the action of impurities in the heat transfer medium, or to a combination of these or other factors.

Accordingly, it is an object of the present invention to provide improved heat transfer media comprising fused salt compositions. A further object is the provision of such improved heat transfer media which will not corrode or otherwise deleteriously 'aflect metallic equipment in contact therewith to any substantial extent. These and still further objects will be apparent from the ensuing description. of my invention. as I was particularly concerned with the problem of carrying out processes of the above designated type employing molten, fluid, inert salts. such as sodium chloride, potassium chloride and salt mixtures such as sodium chloride and potassium 8S chloride and others as heat transfer media. As a result of the thorough investigations and studies which were carriedout in this connection,

it has been found that the above types of salt melts can be used with extraordinary success as 4n heat transfer media if, in accordance with the present invention, care is taken to have present 1 in the melt is. substantial amount of an alkaline material, e. g. an oxide and/or hydroxide f an alkali metal and/or an alkaline earth meta to- 45 gether with a small but substantial amount of of free carbon that will give excellent results for the present purpose corresponds to about 0.5 to 5% and preferably 1 to 3% by weight of the salt melt. Carbon in finely divided form is 55 preferably employed. Examples of the types of ca bon that may be used with good results are wood charcoal, animal charcoal, peat charcoah. activated carbons, graphite, lignite and the like. Inplaceof adding free carbon, substances may be introduced into the melt which, upon heat- 5 ing, carbonize andthereby yield the desired free carbon. Illustrative of such carbon-yielding ma-' terials that may be used are mentioned peat,

wood cuttings and shavings, and similar sub- -structed of iron or steel, at high temperatures,

e. g. at temperatures of 500-1000 C. or higher, without any substantial damage to the apparatus resulting. The salt melts of the present invention are therefore particularly well suited for all purm poses in which they serve as heat transfer media wherein vessels or objects are heated by means of indirect heating. Thus, iron receptacles which are provided with hollow jackets and for which the heating of the inner vessel is carried out in- 25 directly by means of a liquid heating medium present in the hollow jacket or conducted through the same, can be, operated by employing salt melts of the above described type; or conduits, coils, or

the like through which are led theagents-to be 0 heated, can be placed in the melts or conducted through them and the heat transfer thus effect'ed; or, conversely, the melts can be led through the conduits, coils or the like of iron, steel or similar metals and the coils thus used as heating devices. The use ofv the present fused salt heat transfer media .in contact with metal parts asabove suggesteddoes not result in oxidation or other unfavorable reactions taking place on the .vessel wallsor other metal parts.

According to a further modification of the invention salt melts of the type described above may be used to advantage in such a manner that chemical reactions which take place at elevated temperatures are carried out in the presence of or in the melts. For example, fossil fuels such as lignite, peat, and the like may be added to the melt and thus subjected to the desired treatment, e. g. low temperature carbonization or distillation, by heating the melt to a suitable temper-a- 5 ture. Such reactions may be carried out continuously. Thus, finely divided lignite may be introduced into the melt at such a rate and in such amounts that the lignite which is decomposed during the treatment is continuously replaced. In order to avoid an undesired enrichment 'of solid distillation residues in the melt, portions of the salt melt may be withdrawn 'h'om the distillation vessel from time to time and suh= stituted by the addition of fresh melt, or puriiled melt may be returned to the operation. Likewise the melt may be circulated throughout the distillation vessel, e. g. in such a manner that melt with fresh lignite is introduced and the corresponding quantity of melt with solid distillation residues is removed.

The present salt melts may be usedwith metal equipment generally and is especially useful when i the metal equipment is constructed of iron. steel or similar construction materials. Heating of the melt may, of course, be accomplished by any oi the usual methods. I

It will be obvious that many widely diflerent modifications oi the present invention may be practicedwithout departing from the spirit and scope thereof. The invention is therefore not in tended to be limited except as indicated bythe appended claims.

I claim:

1. A fused salt heat transfer medium containing substantial amounts of an alkaline material and finely divided free carbon.

ass. 11,04?

2. A fused salt heat transfer medium containing a substantial amount of an alkaline material selected from the group consisting of the oxides and hydroxides oi the alkali metals and alkaline earth metals, and a substantial amount of finely divided carbon. v

3. A. fused salt heat transfer medium containing about 5 to 10% by weight of an alkaline material selected from the group consisting of the oxides and hydroxides of the alkali metals and alkaline earth metals and 0.5 to 5% by weight of finely divided carbon.

4. a fused salt heat transfer medium containing' about 10% by weight of an alkaline material selected from the group consisting of the oxides and hydroxides of alkali metals and alkaline earth metals and 1 to 3% by weight oi finely divided carbon.

5.. A fused salt heat transfer medium containing about 5 to 10% by weight of caustic soda and 0.5 to 5% by weight of finely divided carbon.

6. A iused salt heat transfer medium containing about 10% by weight of caustic soda and l to 3% by weight of finely divided carbon.

WALTm BECK. 

